In refrigeration systems or air conditioning systems such as used in supermarkets or large buildings, there are usually several refrigeration units, one for each of the refrigeration cases, for example. A large portion of energy costs is spent on defrosting ice or frost from the refrigerated coils. The defrosting is normally done with a manual or electronic timer or facility management system. The use of a timer is very inefficient because the refrigeration is on for a certain time and then the defrosting is on for another period of time. This does not take into account many variables such as the humidity in the air, the ambient air temperature, how full the refrigerator cases are with produce, how much of the cold air is recirculated and how much is lost, the temperature of the product placed in the refrigerated cases, the number of people walking by the cases, how often the doors are opened or left opened, by drafts and currents near the cases, by poorly designed cases with lower openings or air leaks, and many other variable factors. Using a timer, if the humidity is low the defrosting is too often. If the humidity is high there is frost and ice on the cooling unit so it doesn't cool down the refrigerator case as quickly. Accordingly, the timer system of control of defrost will usually have to be set at an average and in the winter dry season or at nighttime in a supermarket, defrosting may be occurring for too long a time and much too frequently. On the other hand during the highly humid days in the summer or during the heavily active daytime hours of the supermarket, the refrigerator coils may build-up a thick coating of frost before defrosting occurs and this thickness of ice reduces the thermal efficiency of the refrigeration unit.